Foundation species promote community stability by increasing diversity in a giant kelp forest

Foundation species structure communities, promote biodiversity, and stabilize ecosystem processes by creating locally stable environmental conditions. Despite their critical importance, the role of foundation species in stabilizing natural communities has seldom been quantified. In theory, the stability of a foundation species should promote community stability by enhancing species richness, altering the population fluctuations of individual species, or both. Here we tested the hypothesis that the stability of a marine foundation species, the giant kelp Macrocystis pyrifera, increased the stability of the aggregate biomass of a phylogenetically diverse assemblage of understory algae and sessile invertebrates that compete for space beneath the giant kelp canopy. To achieve this goal, we analyzed an 18-yr time series of the biomass of giant kelp and its associated benthic community collected from 32 plots distributed among nine shallow reefs in the Santa Barbara Channel, USA. We showed that the stability of understory algae and sessile invertebrates was positively and indirectly related to the stability of giant kelp, which primarily resulted from giant kelp's direct positive association with species richness. The stability of all community types was positively related to species richness via increased species stability and species asynchrony. The stabilizing effects of richness were three to four times stronger when algae and invertebrates were considered separately rather than in combination. Our finding that diversity-stability relationships were stronger in communities consisting of species with similar resource requirements suggests that competition for shared resources rather than differential responses to environmental conditions played a more important role in stabilizing the community. Increasing threats to structure-forming foundation species worldwide necessitates a detailed understanding of how they influence their associated community. This study is among the first to show that dampened temporal fluctuations in the biomass of a foundation species is an important determinant of the stability of the complex communities it supports.

Need for therapeutic drug monitoring in HIV-1 infected children receiving efavirenz doses according to international guidelines

BACKGROUND

International guidelines for the treatment of HIV-1 infected children recommend efavirenz plus nucleoside reverse transcriptase inhibitor combination therapy for first line therapy. Until now little is known about the steady state pharmacokinetics of efavirenz in children.

METHODS

11 HIV-1 infected children at the age of 4 to 10 years received efavirenz according to body weight adjusted dose recommendations at 10 -15 mg/kg body weight. All children were non nucleoside reverse transcriptase inhibitor (NNRTI) naive, 5/11 received efavirenz as first line therapy. Efavirenz plasma concentrations were assessed before daily dose and 1, 2, 4, 8, 24 h post-dose after medication by established HPLC.

RESULTS

7 of 11 children exhibited efavirenz plasma concentrations below targeted ranges. Mean (95% CI) minimum concentrations (C subsetmin) was 1293 ng/mL (range: 889 -1697) and maximum concentration (C subsetmax) was 5552 ng/mL (3951 - 7153) and the mean area under the time-concentration curve at steady state (AUCss) was 63608 ng*h/mL (44222 - 82989). The linear regression analysis of bodyweight adjusted efavirenz AUCss showed a close correlation between dose/bodyweight and plasma concentrations (r superset2 = 0.79). Efavirenz doses below 12.5 mg/kg lead to an AUC < 60000 ng*h/mL in 7 of 8 cases. Higher efavirenz doses exhibited an AUC within the recommended therapeutic range of 60000 - 120000 ng*h/mL (n = 3).

CONCLUSIONS

The data show insufficient plasma concentrations for some children despite efavirenz dosing according to recommendations. Antiretroviral therapy needs to be carefully adjusted in children. Therapeutic drug monitoring is strongly recommended to meet efavirenz plasma levels within the therapeutic range.